Objective To investigate isoforms of LHRH in the primate brain. ABSTRACT:The hypothalamic decapeptide, LHRH, plays the pivotal role in control of reproductive function. Since the first discovery of the LHRH molecule in porcine and ovine brains, 11 additional isoforms of LHRH, all of which are decapeptides, were found widely distributed in the animal kingdom. However, in the brain of higher mammalian species, such as primates, only one form (mammalian form) was discovered, in contrast to the findings that more than one isoforms were present in other vertebrate brains. Recent studies using HPLC analysis in collaboration with Nancy Sherwood as well as immunocytochemistry indicate that His5Trp7Tyr8LHRH, known as chicken II LHRH, is present in the midbrain of fetal and adult rhesus monkeys. Keywords LHRH isoform, mammalian LHRH, chicken II LHRH, midbrain